1. Field of the Invention
The present invention relates to a thermal print head, a thermal printer including the thermal print head, and a printer system including a plurality of thermal printers.
2. Related Art
There has been known a thermal print head or a thermal printer incorporating a thermal print head (see JP-A-No. 2005-186302, for example) that causes the heating resistor to selectively heat recording paper (such as thermosensitive paper) or thermal transfer ink ribbon, so that letters or images are to be printed.
FIG. 16 is a block diagram of an example of the thermal printer including the conventional thermal print head. The thermal printer 990 shown therein includes the thermal print head 999. The thermal print head 999 includes a substrate 991, a heating resistor 992, a driver IC 993, and a connector 994. On the substrate 991, an elongated heating resistor 992 is provided. The thermal print head 999 is connected to a control unit 995 of the thermal printer 990, via the connector 994.
To the thermal print head 999, a printing data signal, control signal, and power necessary for executing a printing action are transmitted from the control unit 995 through the connector 994. The printing data signal and the control signal are transferred to the driver IC 993 through a wiring pattern 996 formed on the substrate 991.
The control signal includes a clock signal, a latch signal and a strobe signal. The clock signal serves to establish synchronization when data to be printed is outputted to the driver IC 993. The latch signal serves to output in parallel the printing data signal serially inputted, by an amount corresponding to one line of the image. The strobe signal serves for supplying power to the heating resistor 992. Here, a printing mechanism such as a platen roller for activating the printing action is not shown in the thermal printer 990 shown in FIG. 16.
The thermal print head 999 is capable of producing a smooth printing action in the case of printing letters and characters containing relatively small data amount. On the other hand, in the case where the data to be printed is, for example, image data that contains gradations of light and intense of black color, the thermal print head 999 executes the following process.
To print the data corresponding to one line for example, the data is outputted to the driver IC 993 the times corresponding to the number of gradations of the image. When the number of gradations is 256 for example, the data for 255 times of printing per line (except for the gradation “0 (=white)”) is transferred from the control unit 995 to the thermal print head 999. To be more detailed, the image data containing the data representing the dots of the gradation “1” and higher is inputted to a shift register (not shown) in the driver IC 993, at a first transfer. Then the image data inputted to the shift register is retained by the latch signal. Then power is supplied according to the strobe signal to the portion of the heating resistor 992 to be heated, determined based on the image data, so that such portion is heated. Thus, the data corresponding to the dots of the gradation “1” and higher is printed on the recording paper.
Then the image data corresponding to the dots of the gradation “2” and higher is transferred, and the similar process is executed. In this case, the dots of the gradation “2” and higher are printed over the dots of the gradation “1”, which have been printed in the first printing process. Such data transfer is executed up to the image data corresponding to the dots of the gradation “255 (=black)”. The transfer action of the image data and the printing action on the recording paper are repeated 255 times respectively. With respect to the dots of the gradation “0 (=white)”, such printing process is not executed. The region on the recording paper corresponding to the dots that have remained unprinted during the printing process from the gradation “1” to the gradation “255” resultantly represents the white portion corresponding to the gradation “0”.
Thus, the thermal printer 990 including the thermal print head 999 has to repeat the transfer action of the image data and the printing action, for printing the image data containing the gradations. This leads to the drawback that the printing takes a long time.
It might be possible to increase the transfer rate of the image data between the control unit 995 of the thermal printer 990 and the thermal print head 999, in order to print the image data at a higher speed. However, an excessively high transfer rate may provoke deformation of the waveform of the signals on respective signal lines between the control unit 995 of the thermal printer 990 and the thermal print head 999, resulting in data deficiency. Besides, radiation may take place in the respective signal lines, which may disturb normal transfer of the signals between each other. Accordingly, a limitation is inevitably imposed on the transfer rate of the image data between the control unit 995 of the thermal printer 990 and the thermal print head 999, and hence it is difficult to transfer the image data at a higher speed. Especially in the case of printing the image data containing an enormous data amount, the printing speed of the thermal print head 999 is subjected to such limitation. Also, the deformation of the waveform and the radiation appear more prominently, as the line length between the control unit 995 of the thermal printer 990 and the thermal print head 999 becomes longer. Therefore, the line length is also limited.
Meanwhile, recently an automatic identification system has come to be widely employed, for example for luggage management at an airport. The automatic identification system automatically takes up the data of the objects to be managed, by means including both hardware and software without depending on human power, and recognizes the data of the object. Specific examples of the automatic identification system include the one that utilizes a Radio Frequency IDentification (RFID) tag. The RFID tag includes a memory for recording the identification data, and a medium-side coil antenna for data transmission/reception by wireless communication, and letters or a barcode representing the identification data is printed on the outer surface of the RFID tag. To execute the data transmission/reception to and from the RFID tag, and the printing thereon, for example an RFID tag printer is employed (for example, JP-A No. 2003-132330).
However, the RFID tag printer has to be equipped with the antenna for data transmission/reception and a driver IC therefor, in addition to the thermal print head engaged in the printing function. Especially in the case where the antenna is located distant from the RFID tag, the print target, the reliability of the data transmission/reception may be degraded.